Shock strut



July 30, 1940. c. v. JoHNsoN snocx sTnUT Filed oct. 11. 1954 3 Sheets-Shea@ 2 July 30 1940- c. v. JoHNsoN 2,209,603

sHocx sTRuT Filed Oct. 11, 1934 3 Sheets-Sheet 3A sie w u v333 3 vl s m s .m w 1 e a a a s. a

Patented July 30, 1940 UNITED STATES 2,209,603 SHOCK STRUT Carl V. Johnson, South Bend, Ind., assignor to Bendix Products Corporation, South Bend, Ind., a corporation of Indiana Application October 11, 1934, Serial No. 747,993

Claims. (Cl. Ztl-bel) This invention relates to shock struts,and more particularly to shock struts designed for use -in aircraft landing gears, and particularly a shock strut which is adapted to resist or transmit twist- 5 ing forces as well as the usual compressive forces.

In aircraft landing gears it has been found desirable to employ shock struts which can transmit twisting or torsional forces so that each strut may project from the planeindependently of any other strut and be free from cross axles or torsional braces fixed to the lower extremity of the strut, which braces, when heretofore ern-v ployed, were necessarily connected to the movable part. The present invention is directed to 1B struts of the telescopic chamber type wherein means are provided to resist torsional or twisting forces through the strut, and an important feature, among others, is the provision of such means which will be wholly enclosed, free from wear due to abrasive action of grit, dirt and other foreign matter.

It is accordingly an object of the invention to provide a shock struthaving telescopic casings wherein improved means are ,provided to resistV torsional or twisting forces throughout the stroke without interfering with the normal shock absorbing function.

A further object of the invention is to provide an improved shock strut having telescopic casings wherein splines are provided to resist torsional or twisting forces, the splines being so arranged as to be protected from exposure.

A further object of the invention is td provide an improved shock strut having telescopic casings and employing damping liquid with means to transmit twisting or torsional forces from one end to the other and employ the damping liquid as a lubricant for the means.

A further object of the invention is to provide w in a shock strut of the telescopic casing, metering pin orifice type, means to prevent relative rotation of the parts so that the metering pin and its relation to the orifice may notxbe disturbed.

Still another object of the invention is to provide a shock strut having splined members which is of simpliied construction, rugged and able to withstand the stresses incident to landing and taxiing, and particularly in which the splined 50 members are easily formed.

' y The above and other novel features of the invention will appear more fully hereinafter from the following detailed description when taken in conjunction with accompanying drawings. It is expressly understood, however, that the drawings are employed for purposes of illustration only and 'are not designed as a definition` of the limits of the invention, reference being had for this purpose to the appended claims.

In the drawings wherein like reference nu- 5 merals indicate like parts: e

Fig. i illustrates a longitudinal section of one form of shock strut embodying certainl features of the invention; s

Fig. 2 is a section taken on line 2 2 of Fig. i 10 illustrating certain details of the lower end of the strut;

Fig. 3 isa section taken on the line 3 3 of Fig. l showing the details of the interengaging splines of Fig. 1; 15

Fig. 4 illustrates a longitudinal. section of a modied form of shock strut showing certain features of the invention; l y

Fig. 5 illustrates a.V longitudinal section of another modiiied form of shock strut and illustrates 20 certain features of the invention in a slightly varied form; 4 y

Fig. 6 is a side elevation of the top portion of the strut of Fig. 5;

Flg. 7 is a section through the spline taken on 25 the line lof Fig. 5;

Fig. 8 is a side elevation of the lower end of the strut of Fig. 5;

Fig. 9 is a longitudinal section of a .further modified form of shock strut; f 30 Fig. 10 is a top view of the strut of Fig. 9, and

Fig. 11 is a horizontal section through the bottom of the strut taken on the line l i-i l.

Referring to the drawings, and particularly Fig. 1, there is shown a shock strut having upper 35 and lower tubular casing members I0 and l2 respectively, the upper member being adapted to be secured in a well known manner to the fuselage or framework of an airplane. n The lower casing member I2 is provided at its lower end with a 40 short horizontal stub axle Il which is adapted to carry thereon a common form of wheel, not shown, suitable for aviation landing gear. The upper casing member I0, which telescopes within the casing member I 2, is provided with apiston I8 at its lower end, which piston has an inturned ange 20, which is threaded into the interior of the casing member l0, the flange 20 being pro-- vided with an external shoulder 22 adapted to abut the end of the casing I0 when screwed in 50 place. Within and' adjacent the upper end of the casing is a bulkhead or diaphragm 24, which may be screwed in place against an annular internal shoulder 26. in the wall of the casingl, the diaphragm having for the purpose lugs 2l 55 adapted to be engaged by a suitable turning tool.

The piston |8 is preferably provided with a hardened bushing `30 having an orifice 3| set in an aperture in the center of the piston, and a housing tube 33 which extends upward' and covers the oriiice 3| of the bushing, is securedto the piston together with the bushing 30 by suitable fastening means such as screws 32.

In the bottom of the casing member` I2 is provided an end closure member 34 which is threaded into the lower end of the casing member, the latter preferably being outwardly offset slightly to provide a shoulder for the end closure to ab'ut when screwed in place.` Preferably, to assure against possible relative rotation between the end closures in the casing I2, the members are welded together by flowing metal in the annular groove 36 between the end of the casing and the corresponding shoulder 38 on the end closure member.

In order to vary the eiective area of the orice 8| carried by the piston' |8, a metering pin 40 having a suitable contour is secured at its lower end to the end closure member 34 and projects upward and through the orifice and cooperates therewith to change the effective area as the members reciprocate. The housing member 33 which is of approximately the length of the metering pin 40, is provided with a one-way valve 42 in its top and bleed apertures 44 in the side to permit free iiow of fluid upward but control the flow of uid through the orice in reverse direction.

The upper end of the outer casing member I2 is provided with an enlarged diameter offset por-v tion 46 in which is arranged a packing retaining ring 48 which rests against the shoulder 50 formed by the oiset, packing material 52 and a packing nut 54 which is provided with suitable lugs 56 for engaging a suitable tool. The casing member I is provided with a smooth external wall 58 which is adapted to slidably engage the packing and cooperate therewith to prevent any leakage during the operation or use of the strut.

In order to simplify the construction of the landing gear in the bracing thereof, the axle I4 is secured directly to the end closure member 34 by means of the lugs 60 and 62 formed integral. with the end closure member. A plate such as 64, to which may be secured braking members or a brake backing plate as will be well understood in the artis splined on the axle as at 66, as best shown in Fig. 2.

To resist torsional force, or twisting eiect on the strut resulting from the shocks of landing and the eiect of braking the rotation of the v landing wheels, the casing members I2 and I0 are provided with interengaging splines. The casing member I2 is provided, as shown, with splines extending from the end closure member 34 to the packing located at the upper end. The casing member I0, which reciprocates within the casing I2, is provided with a shorter spline 'I2, which splines are located adjacent the piston end of the casing and extend to the smooth surface 58 provided for engagement with the packlng. The splines 'l2 preferably end abruptly and form a shoulder for engaging the packing retaining ring 48 to limit the extending movement between the casings I0 and I2 when the strut is unloaded, or extended.

The lower casing I2 of the strut, in practice, is' substantially filled through a ller plug -14 withv a hydraulic damping liquid "which, upon. landing, is forced through the orifice 3| to absorb shocks. It will be observed that the splines 16 and 12 are thus exposed to this damping liquid since the same are within the end closure formed by the casing I0 and |2 and the packing 46, and thepresence of the damping liquid tends to lubricate the splines and protect the same from undue wear.

A modified form of strut; as shown in Fig. 4, wherein the upper casing member is outside of the lower casing member whereby a longer portion of-the strut may be braced rigidly to the body or framework of the airplane, comprises an outer upper casing member 0 and a lower inner casing member ||2. In order to conserve on the length of the strut and still provide substantial overlap of the telescoping members, an

linternal tubular member ||4 is provided which is adapted to move simultaneously with the casing |I0, the lower casing member ||2 reciprocating between the tubular member |I4 and casing The lower casing member ||2 comprises an end sleeve I|6 having an inwardly oiset section I I8 at the upper end thereof over which is secured by welding a tubular member extending upwardly into the strut and threadedly carrying an inner guide collar |22 at its upper end.

Seated on an internal shoulder |24 in the oiset portion of the sleeve ||6 is a diaphragmr or end closure |26 which is adapted to carry a metering pin |28 varying in contour as at |36.

The tubular member ||4, which is secured to theupper end of the strut and upon which the guide collar |22 slidably bears, carries at its lower end a piston |36 having an upwardly-extending ange |38 which is threaded on the exterior of the tubular member ||4 and is keyed against rotain'on .by a set screw |40 to prevent loosening. The piston |36 is provided with a hardened center piece |42 having an orifice |44 therein which is adapted to cooperate with the metering pin |28 and its variable contour |30, to effect a gradual change in the effective area of the orifice with relative movements. On the top side of the piston |36 is provided a tubular housing |46 having a ap valve |48 on the top thereof and one or more bleed ports |50 in the side wall.

The tubular member 4 is secured to the casing ||0 by means of a flanged end closure |62 threaded and welded thereto as at |53 and a shouldered collar member |54 threaded to the latter and engaging an internal shoulder |56 of the end cap |58 forming the upper part of the casing IIO. Pins |60 passing through the cap |58 and collar |54 secure the parts. A ller tube |62 having a plug is passed through the end closure |52.

To prevent leakage between the tubular member I|4 and the casing II2, packing |64.is arranged on the tubular member ||4 between the ange |38 of the piston and a packing retaining ring |66, which is held in any adjusted position by the nut |68 and lock nut |69 threaded on an exteriorly raised threaded portion |I5 of the tube ||4. The nut |68 is undercut as at |1| so that it may extend beyond the threads to the smooth portion of the tube I|4 carrying the packing.

The lower end of the strut is shown as provided with a flanged member which is secured to the sleeve ||6 by means of pins or bolts |82, and to resist twisting movements or torsional stresses'imposed upon the strut by alanding wheel or its brake secured to the angle ange member |80, interengaging splines are provided between the casing members Ill and |I2, the casing member ||2 being preferably provided at its upper end with splines |86 greater in length than the strut stroke. I'he member IIB is shown as provided with a collar having a bearing portion |88 and complementary splined portion |90. 'I'he bearing portion is sho'wn as resting against a shoulder |92 in the interior of the casing member and keyed to the casing by a plurality of pins such as |94.

The maximum extended position of the strut may be regulated by a suitable stop or bumper which may be seated against a shoulder |23 in the side wall of the member ||4. As shown the bumper comprises an annular ring |26 upon which may be'seated a rubber ring |21 in which holes |28 are provided to permit compression of the rubber to absorb shock when the same suddenly engages the collar |22.

There is illustrated in Fig. a modified form of strut which is similar to but represents an inversion of the modiiication of Fig. 1. The same comprises, in general, an outer`upper casing member 2||| and an inner lower casing member 2|2 arranged to reciprocate with respect to one another. 'Ihe lower casing member 2|2 comprises a wheel axle end fitting 2|4 secured by bolts 2|6'to a. tubular member- 2|8 having a smooth packingengaging exterior surface 228. Internally near the upper end of the casing 2l2 is carried a rigid diaphragm 222 seated on an annular internal shoulder 226.

The outer casing member 2|6, as shown, is constructed of a plurality of tubular members and comprises an end cap 236 having a cylindrical ange secured within an upper tube portion 232 by means of pins 234 and an annular weld 236 thereby providing an upper air chamber.

Against the lower end of the tubular member 232 is seated a. plate 234 having an orice 236 and sleeved on the outside of the lower end of the tubular member 232 is a short tubular member 238 to which is keyed by Pills 240 the main .tubular member 242 which extends downward over the inner lower casing member 2|2. The tubular members 232 and 238 are welded together at each end of the member 238 and the same form a shoulder in the main tubular member 242 for the piston 234. At the lower end of the tubular member 242 there is provided an enlarged offset portion which providesa space for a packing including a packing retaining ring 244, washers 246, pressure members 2,48 and a` packing nut 250, the packing engaging the smooth exterior surface 228 on the tubular member'2l8.

As similarly described in connection with the other modications, the diaphragm 222 carries a metering pin of a chosen contour which is adapted to cooperate with the orice 236. To control the return ilow of iluid through theorice, a housing member 262 having a' flap valve 264 and one or more bleed ports 266 is provided.

In order to prevent relative rotation between the casing members 2|0 and 2|2,- the main casing member 2in on its inner surface is splined for a considerable distance between the plate or diaphragm 234 and the packing chamber in the lower end. The casing member 2I2 is slightly reduced in its exterior diameter and is splined for the reception of a cylindrical member 21| having internal and external splines complemental to the splines of members 2|2 and 2|! respectively. This latter cylindrical splined member is suitably secured by pins 216 to the casing member 2l2 and seats against a flange 292 on -a sleeve member `29|), which in turnengages the shoulder formed bythe reduced diameter splined portion of casing 2|2. The cylindrical splined member 21| is constructed of a special metal for slidably engaging the internal splines? of the member 2|0. 4

In order to brace the upper casing member 2|@ suitable belly bands 280 and 282 are provided to which may be secured guy wires and brace rods. J

A further modification is illustrated in Fig. 9 wherein the upper air chamber com-prises the outer casing member, the construction being such that'the upper casing member may be conveniently braced over its entire length, since all reciprocating parts are within. 'I'his latter featureis also true of the structures ofFigs. Il and 5.

'Ihe construction comprises an upper outerv cylindrical casing member 3|0 yprovided at its upper end with an end closure member 328 and an external sleeve 326 having attaching lugs 321,-A

the sleeve'being secured to the strut end by taper threaded into the lower end of the casing member 3|0.

Arranged to reciprocate within the outer upper casing member isa second lower reciprocating casing member 3I2 of cylindrical form, the latter slidably engaging the packing of the casing 3|8 in uid tight manner. 'Ihe lower end of the member 3|2 is shown as provided with a wheel axle 313.

The inner wall of the casing 3|!) is provided with splines 3|6 which'are adapted to engage complementary splines of a sleeve 3|8 secured to the upper end of the casing 3|2, the sleeve being preferably splined on the latter and-secured by the threaded collar' 320. Relative rotation is thus To prevent the drawing of a vacuum in the prevented between the members 3|2 and annular space between the casings 3|Il and 3|2,

the packing and the inner engaging splines which vacuum might suck air past the packing 329', and yet to permit a snug sliding fit between the spline members so they may not act as an orifice, one or more splines may be-omitted on one member without the omission of its corresponding groove on the other member, thereby aiording free communication between the chambers and the annular space leading to the packing. Such an arrangement is illustrated in conjunction with the modication of Fig. 5 in Fig. 7 by theunlled grooves 213 and may'obviously be applied to the other modifications, and particularly those o1' Figs. l and 9.

Depending within and from the upper end of Athe inner casing member 3|2, is an inner tube to cooperate with the metering pin 344, and reciprocate in the inner tube 340, the piston being supported from the end closure member 324 at the top of the casing member 3|II, by meaas of a tube 356 which is suitably perforated along its length as at 353 to permit free ow in and out thereof. The tube 356 is secured to the end closure member 324 by a iiange plate 360, having a central aperture through which extends a filler tube 362 arranged centrally in the end closure 324.

A tubular housing 364 with a check valve 366 therein is secured over the orice 352, and provides a housing forvthe metering pin. An orifice or bleed port 366 may be provided in the housing to permit gradual extension of the strut, rapid extension being prevented or snubbed by the closing of the check valve,

Maximum extension of the strut is controlled .by a shoulder 380 on the casing member 3l2 which is adapted to engage the packing retaining ring 330. thus limiting movement between the In operation, each of the modifications is sim- 'ila'r in that \upon landing, liquid which lls the strut to a level above that of the orice is forced from'the lower chamber below the orifice carrying member through its orice and through the one-way valve into the upper chamber further compressing air in the top which is already under a suitable high pressure in the order of 30 or 40 atmospheres, the pressure depending upon the diameter of the strut and the weight to be carried. After the initial shock has been absorbed, the compressed air supports the load of the plane resiliently during taxiing and the flap valve 264 prevents the compressed air in the strut from causing rebound since the bleed ports 266 are provided to regulate the rate of extension of the strut after the initial shock has been absorbed and the strut tends to extend gradually to an equilibrium, such that the air pressure within is just suflicient to support the load. When the airplane takes oi and the load is relieved, the modification of Fig. 1 is such as to permit the strut to extend until the shoulder formed by the end of the splines engages the packing ring, after which further extension is prevented except that permitted by the compressibility of the packing. Fig. 5 is similar in this respect except that the annular spacer sleeve 290 engages the packing retaining ring. In Fig. i the annular rubber ringi |21 provides a limit for the extension movement, Fig. 9 is like Fig. 5.

It will thus be seen that a shock strut is provided wherein relative rotation between the members is prevented and the structure provided therefor is totally enclosed and in the modifications of Figs. 1, 5 and -9 is subjected to the lubricating qualities of the damping liquid employed in the strut itself. Thus the wearing surfaces are enclosed and protected from the entrance of foreign matter and are maintained against undue wear. As will now be readily appreciated such a strut permits the mounting of a wheel directly upon a bracket rigidly secured to the lower telescopic member and such a construction merely requires that the upper telescopic member be adequately secured and braced to the fuselage or wing of the plane thereby permitting the independent mounting of one wheel with respect to the other and also doing away with the necessity of interconnecting axles or providing torque arms extending to the movable or reciprocable part of the shock strut.

Although but four embodiments of the invention have been illustrated and described, it is to be understood that the invention is not to be-limited thereto but may be embodied in other mechanical arrangements and forms. For example, the various features of any one of the modifica- 1 tions might be substituted for those of the other modifications. As such and other changes in construction and arrangement may be made Without departing from the spirit of the invention as will be apparent to those skilled in the art, reference will be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. A shock absorbing strut for aircraft comprising a pair of telescopic tubular members, the outer member being closed at its lower end, having a packing on its upper end, and having internal splines extending substantially from the lower end thereof to the packing, the inner member being closed adjacent its upper end, and having an orii'lced piston at its lower end, said lower end having a sleeve secured thereon which is provided with external splines adapted to engage said internal splines and prevent rotation between the members.

2. In a fluid shock absorber, inner and outer telescoping cylinders, the inner cylinder having a smooth exterior except at its inner end and the outer cylinder having a packing at its inner end engaging over said smooth exterior, the inner cylinder having removable and replaceable splines at its inner end, and the outer cylinder having relatively extensive spline grooves behind said packing.

3. In a shock absorber, a pair of telescoping cylinders having interengaging spline portions, the spline portion of one cylinder being in the form of a sleeve attached to its cylinder in a manner to prevent rotation thereupon, and formed of'a different metal than the other spline portion..

4. In a shock absorber, a pair of telescoping cylinders, one of said cylinders having an integral spline portion, and the other cylinder having a sleeve spline portion attached thereto and secured against rotation thereupon, and cooperating with said rst named spline portion, the spline portions of the two cylinders being formed of different metals.

5. In a shock absorber, a pair of telescoping cylinders, one of said` cylinders having an integral spline portion, and the other cylinder having a sleeve spline portion attached thereto and Isecured against rotation thereupon, and cooperating with said first named spline portion, said sleeve being formed of a different metal from that of the rst named cylinder.

CARL V. JOHNSON. 

